The invention concerns a method and an apparatus for determining the impressing depth of a tire on a motor vehicle wheel.
In this specification the term impressing with of a disk wheel of a motor vehicle is used to denote the axial spacing between the inside surface of the disk portion of the wheel, being the surface which in the mounted condition of the wheel bears against a mounting surface on the hub of an axle of a motor vehicle, and the center of the rim width. That dimension can also be referred to as rim offset.
When converting the tires fitted to motor vehicles, in particular to change over to wide tires, rims or disk wheels with different impressing depths for the front and rear axles of the vehicle are frequently used when fitting the new tires to the motor vehicle wheels. As however the disk wheels involved are often of the same external appearance, there may be a risk of confusion occurring between them, so that the front and rear axles of the vehicle are fitted with the wrong wheels.
An object of the present invention is to provide a method of determining the impressing depth of a tire on a motor vehicle disk wheel, with which that dimension can be easily and reliably ascertained.
Another object of the present invention is to provide a method of determining the impressing depth on a motor vehicle disk wheel, which can be carried into effect by a simple operating procedure which can be implemented quickly and which gives accurate measurement results.
Still another object of the present invention is to provide an apparatus for determining the impressing depth of a tire on a motor vehicle disk wheel which while being of simple structure affords rapid and reliably accurate results.
In accordance with the principles of the present invention in the method aspect the foregoing and other objects are attained by a method of determining the impressing depth of a tire on a motor vehicle disk wheel, wherein the disk wheel is arranged on a main shaft of a wheel balancing machine, with the disk wheel having its inside disk surface bearing against an abutment surface which is fixed with respect to the shaft. The rim width of the disk wheel is ascertained. The impressing depth is determined from the rim width and the respective spacing of the abutment surface and a measurement point at the rim from a reference plane on the machine. The measurement point at the rim can be one of the two rim flanges of the disk wheel or measurement points of the rim width.
In the apparatus aspect the foregoing and other objects are attained by an apparatus for determining the impressing depth of a tire on a motor vehicle disk wheel, comprising a wheel balancing machine structure having a main shaft for mounting a motor vehicle wheel thereon, and sensing means for sensing geometrical data of the wheel mounted on the main shaft and for determining axial spacings of given parts of the wheel with respect to a reference plane of the machine. The apparatus further includes an evaluation means for determining at least one balancing vector such as balancing mass or balancing angular position in dependence on the ascertained geometrical wheel data and measurement values obtained during a measurement operation. A display means is provided for effecting balancing of the wheel. The apparatus further includes a computing means connected to the evaluation means, and operable to compute the impressing depth from the respective axial spacing of a measurement point at the rim of the wheel and the abutment surface on the machine main shaft against which the wheel is mounted, from the reference plane, and the rim width. The measurement point at the rim of the wheel may be one of the rim flanges or measurement points of the rim width.
As will be seen in greater detail from preferred embodiments of the invention which are described hereinafter, the invention involves the use of a wheel balancing machine which is required in any case in a motor vehicle workshop. The sensing means of the apparatus for determining the geometrical data of the wheel which are required for setting the electronic evaluation system of the wheel balancing machine to the respective motor vehicle wheel to be balanced, and the geometrical data, can also be employed for the purposes of the invention.
In accordance with the invention therefore the impressing depth can be ascertained from the wheel rim width and the spacing between an abutment surface, in particular of a disk-shaped configuration, which is provided on the main shaft of the wheel balancing machine and which extends perpendicularly to the axis of rotation of the main shaft and against which the disk wheel bears with the inside mounting surface of its disk portion in the unbalance measuring operation, and a reference plane which is fixed with respect to the machine, and also from the spacing between for example one of the two rim flanges of the wheel or one of the two measurement points for the rim width, and the above-mentioned reference plane.
The reference plane referred to above can be the plane from which the spacings of the motor vehicle wheel to be balanced, its rim flanges, and its balancing planes are ascertained, for example by operation of suitable sensing means. Sensing means of that kind, for example in the form of a rim width sensing device or in the form of measuring sensing members mounted displaceably on the balancing machine for sensing the inner and outer rim flanges of a wheel can be found for example in the operating instructions for the Geodyna 88/88 m wheel balancing machine from Hofmann, imprint 941214509.86.
The above-mentioned geometrical data which are inputted into the electronic evaluation system for determining the respective balancing vector involved in the corresponding balancing plane on the motor vehicle wheel can be evaluated to determine the impressing depth of the wheel and can be displayed by a display unit provided on the machine. In that way the service operator is given information as to the axle, either the front axle or the rear axle, of the motor vehicle, at which the motor vehicle wheel which is possibly being balanced at the same time has to be mounted.
Further objects, features and advantages of the invention will be apparent from the following description of preferred embodiments thereof.